Pressure equalizing arrangements

ABSTRACT

This invention relates to arrangements for equalising the pressure between two locations, at least one of which is subject to pressure variations in the conditions prevailing therein, and which include a common structure extending therebetween. The invention is particularly concerned with an arrangement for equalizing the pressure between two sealed housings one of which contains air and the other of which provides an oil reservoir which is subject to pressure variations. A bellows is mounted in the oil reservoir and its interior is in connection with the other housing through a connector providing a flameproof path mounted in a common partition wall. The arrangement greatly simplifies the seals required for a shaft extending through the common partition wall as a pressure differential across the seals is substantially eliminated.

[111 3,817,034 [4 June 18, 1974 PRESSURE EQUALIZING ARRANGEMENTS Peter Thomas Mence Nott, Bath, England Assignee: Rotark Limited, Somerset, England Filed: Mar. 9, 1973 Appl. No.1 339,711

Inventor:

References Cited UNITED STATES PATENTS 6/194'4 Kirkland 60/478 x 2/l952 Dearsley 60/478 X 3/1953 Grebe 60/329 X l/l959 Haley 60/DIG. 10

Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT This invention relates to arrangements for equalising the pressure between two locations, at least one of which is subject to pressure variations in the conditions prevailing therein, and which include a common structure extending therebetween. The invention is particularly concerned with an arrangement for equalizing the pressure between two sealed housings one of which contains air and the other of which provides an oil reservoir which is subject to pressure variations. A bellows is mounted in the oil reservoir and its interior is in connection with the other housing through a connector providing a flameproof path mounted-in a common partition wall. The arrangement greatly simplifies the seals required for a shaft extending through'the common partition wall asa pressure differential across the seals is substantially eliminated.

10 Claims, 2 Drawing; Figures 1 PRESSURE :EQUALIZING ARRANGEMENTS This invention relates to arrangements for equalizing the pressure between two locations, at least one of whichissubjectto pressure variations in the conditions prevailingtherein, and which include a common structure extendingxtherebetween.

In particular, the invention relates to the provision of pressure equalizing arrangements between two locations, .atleast one of which comprises a sealed housing or vessel subject to pressure variations in the conditions prevailingtherein and which includesa shaft assembly extendingrtherefrom intothe other location.

The second location need not be sealed and could be the atmosphereas would be the case in the application of the invention to the sealed fluid-tight chamber of a hydraulic gear box. The invention is, however, more .particularlyapplicable to assemblies where the second location is also a sealed housing or vessel but which is not normally subject to any substantial pressure variations in the conditions prevailing therein. A particular example of suchan arrangement is an electro-hydraulic actuator, e.g. as described in our co-pending US. Pat. application No. 175,864, now US. Pat. No. 3,753,350, in which an electric motor is drivably connected by a shaftassembly with a hydraulic pumpfor providing the pressure fluidfor operating the hydraulic servo motor connected to the output member. The electric motor is located 'in a sealed housingwith the other electrics of the actuator, while the hydraulic pump is located in a second housing which providesareservoir and is sealed so asto enable the actuator to be mounted in any desired position. The shaft assembly extends through a partition wallbetween the housings and to compensate for expansion and/or contraction of the hydraulic fluid in the second housing some means, such as a gas-filled bladder, isprovided in the reservoir.

An object of the present invention is to provide a pressure equalizing arrangement which will substantially eliminate pressure differentials across the shaft assembly due to differences in the pressures prevailing in the two locations. The provision of such a pressure equalizing arrangement greatly simplifies the seals required for the shaft assembly while compensating for the expansion and/or contraction of the fluid in the sealed location.

According to the invention there is provided an arrangementcomprising two locations, one of which is a sealed housing or vessel containing a fluid subject to pressure variations, a common structure in said sealed housing or vessel and extending therefrom into said second location, and pressure equalizing means in said sealed housing or vessel comprising a member deformable in response to expansion or contraction of said fluid in said sealed housing or vessel, said member communicating with said other location so as to eliminate pressure differentials across the common structure between said locations.

In a preferred embodiment of the invention the pressure equalizing means comprises a sealed bellows mounted in an actuator for eliminating pressure differentials across a shaft extending between two housings one of which contains an electric motor while the other contains a hydraulic pump which is drivingly connected with the electric motor by the shaft. The bellows is mounted in the pump housing which contains a hydraulic fluid and the interior of the bellows communicates with the interior of the motor housing by a connector mounted in the common wall between the housings and which provides a sealed flameproof path for the flow of air to and from the motor housing as the bladder contracts or expands in response to expansion or contraction of the volume of hydraulic fluid in the pump housing. In this way the hydraulic fluid in the pump housing can expand or contract with variations in temperature without causing apressure differential across the seals etc. of the shaft assembly.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. I is a simplified layout of an electro-hydraulic actuator of the kind described in our copending US. Pat. application No. 175,864 and which is fitted with the pressure equalizing arrangement of the invention, and

FIG. 2 is an enlarged view of the flameproof connector for the equalizing arrangement which may be open to atmosphere or as shown in FIG. 1.

Referring to the drawings the actuator shown is basically electro-hydraulically operated, the mechanism being contained in a casing which comprises a first or mainhousing 10 which for convenience is shown in the drawing as being positionedvertically, but as will be hereinafter explained can be located in any desired position. The housing contains a hydraulic servo-unit or motor 11 consisting of a piston 12 which is slidably mounted in annular wall 13 of the housing 10. The piston 12 is connected to or formed integrally with an output member for the actuator. The output member comprises a shaft 14 which extends across the housing 10 and projects at one end through the end mounting face 15 and at the other end through the end mounting face 16. The projecting ends of the shaft 14 are provided with connections 17 for coupling one or other end of the shaft to the member to be controlled such as a valve (not shown). The shaft may be connected at either end depending on the direction of control and/or the mounting of the actuator.

The housing 10 is completely filled with a hydraulic fluid and the ends of the shaft 14 extend through the end faces l5, 16 of the housing in sealing-tight manner by the provision of suitable sealing rings 18. The housing 10 is sealed so as to permit the: mounting of the actuator in an inverted or any other position.

The housing 10 contains a hydraulic pump 19 which when operable pumps hydraulic fluid through passageway 20 to the high pressure chamber 21 in the cylinder 13 between the piston 12 and end mounting face 16 of the housing. The piston 12 on its low pressure side is provided with an annular skirt 22 which acts as a support for one end of a heavy coiled] compression spring 23 the other end of which seats on a retainer 24.

The pump 19 is operable to move the output shaft 14 upwardly as shown against the action of the spring 23 which acts to return the output shaft downwardly when the pump is inoperable and the chamber 21 is connected to the low pressure side of the piston 12. The

low pressure side of the piston provides a hydraulic fluid reservoir which is subject to expansion and contraction in response to temperature changes. Such expansion and contraction of the fluid in the sealed housing 10 results in pressure changes in the housing which are compensated by the provision of a deformable bag in the form of a bladder or bellows 25 made of rubber or like material and which is supported by retainer 24 in an extension 26 of the housing 10. The bladder or bellows 25 also provides a device, as will be hereinafter explained, for equalizing the pressure between housing 10 and a second housing 27 which is mounted transversely on housing 10. v

The housing 27 contains a gaseous fluid, such as air, and its interior is directly connected with the interior of the bladder or bellows 25 by means of a flexible hose 28 which is connected at one end to the bladder or bellows 25 and at the other end to a connector 29 mounted, as will be hereinafter described, in the partition wall 30 forming part of the housing 27. The housing 27 is provided with a closure portion 31 and the housing contains electric induction motor 32 which is drivably connected with the pump 19 by means of a shaft assembly 33 which extends through the partition wall 30 in an elongated mounting 34 projecting from wall 30 into the housing 27.

The function of the bladder or bellows 25 in equalizing the pressures in the housings l and 27 has the advantage of eliminating any pressure differentials over the shaft assembly 33 which might occur between the housings due to expansion and contraction of the hydraulic fluid in housing due to temperature changes. The invention thus enables a simple mounting to be provided for the shaft assembly without the necessity of complicated pressure seals. As shown, the shaft 33 is mounted in spaced bearings 35, 36 in mounting 34 which is fitted with an end seal 37 for fluid tightness.

The connector 29 in wall 30 is shown more clearly in H6. 2 and provides a flameproof path for the flow of air between the interior of bladder or bellows 25 and the interior of housing 27 or, in an alternative embodiment, to atmosphere. To this end, the connector 29 comprises an elongated sleeve 38 which is mounted in an apertured boss 39 in wall 30. The sleeve 38 has a central passageway 40 stepped to provide three sections having different diameters. The section of smallest diameter atone end communicates directly with the interior of the housing 27 while the section of largest diameter at the other end of the sleeve is adapted to receive one end of coupling 41 the other end of which receives the end of hose 28. The coupling is retained in the sleeve by a retainer 42 which is threadably attached to the sleeve.

The sleeve 38 is stepped also on its outer surface to provide a shoulder 43 engaging the wall 30 in housing 10 and the sleeve is fixedly mounted in the wall 30 by means of a nut 44 threadably attached on the sleeve at its other end in housing 27. The connector 29 is completed by a fine bore filter 45 located in the section of the passageway 40 of intermediate diameter.

In the event of expansion or contraction of the by draulic fluid in the reservoir of housing 10 as a result of temperature changes, the bladder or bellows 25 in the reservoir will contract or expand so as to expel or withdraw air into or from the electrical housing 27. The

compensating change in the pressure in the air in the electrical enclosure will result in a substantial equalization of the pressure differential across the shaft 33 and- /or control rods extending through the common partition wall 30. The arrangement thus allows for varia: tions in the pressure in the hydraulic fluid without causing any substantial pressure differential across the seals on the shafts and/or control rods extending through the common partition wall 30 between the two sealed housings 10 and 27.

I claim:

1. An arrangement comprising two locations, one of which is a sealed housing or vessel containing a fluid subject to pressure variations, a common structure in said sealed housing or vessel and extending therefrom into a second location, and pressure equalizing means in said sealed housing or vessel comprising a member deformable in response to expansion or contraction of said fluid in said sealed housing or vessel, said member communicating with said second location so as to eliminate pressure differentials across the common structure between said locations.

2. An arrangement as claimed in claim 1, wherein the pressure equalizing means comprises a sealed bellows in said sealed housing or vessel, the interior of said bellows being directly connected to the second location for the flow of fluid to and from said second location in response to expansion or contraction of said bellows.

3. An arrangement as claimed in claim 2, wherein said one location is a sealed housing or vessel containing hydraulic fluid.

4. An arrangement as claimed in claim 3, wherein the second location is atmosphere.

5. An arrangement as claimed in claim 3, wherein the second location is a second sealed housing or vessel containing air.

6. An arrangement as claimed in claim 4, wherein the common structure is a shaft assembly.

7. An arrangement as claimed in claim 5, wherein the common structure is a shaft assembly.

8. An arrangement as claimed in claim 7, wherein the shaft assembly extends through a common partition wall between the two sealed housings or vessels and the interior of the sealed bellows is connected with the interior of said second sealed housing or vessel by means of a connector mounted in the partition wall.

9. An arrangement as claimed in claim 8, wherein the second sealed housing or vessel contains an electric motor drivingly connected by said shaft assembly with a hydraulic pump in said first sealed housing or vessel, said first sealed housing or vessel forming a hydraulic reservoir for said pump which is operable to actuate a servo motor, said connector including a flameproof path for the passage of air therethrough.

10. An arrangement as claimed in claim 9, wherein said servo motor operates an output member.

l l l 

1. An arrangement comprising two locations, one of which is a sealed housing or vessel containing a fluid subject to pressure variations, a common structure in said sealed housing or vessel and extenDing therefrom into a second location, and pressure equalizing means in said sealed housing or vessel comprising a member deformable in response to expansion or contraction of said fluid in said sealed housing or vessel, said member communicating with said second location so as to eliminate pressure differentials across the common structure between said locations.
 2. An arrangement as claimed in claim 1, wherein the pressure equalizing means comprises a sealed bellows in said sealed housing or vessel, the interior of said bellows being directly connected to the second location for the flow of fluid to and from said second location in response to expansion or contraction of said bellows.
 3. An arrangement as claimed in claim 2, wherein said one location is a sealed housing or vessel containing hydraulic fluid.
 4. An arrangement as claimed in claim 3, wherein the second location is atmosphere.
 5. An arrangement as claimed in claim 3, wherein the second location is a second sealed housing or vessel containing air.
 6. An arrangement as claimed in claim 4, wherein the common structure is a shaft assembly.
 7. An arrangement as claimed in claim 5, wherein the common structure is a shaft assembly.
 8. An arrangement as claimed in claim 7, wherein the shaft assembly extends through a common partition wall between the two sealed housings or vessels and the interior of the sealed bellows is connected with the interior of said second sealed housing or vessel by means of a connector mounted in the partition wall.
 9. An arrangement as claimed in claim 8, wherein the second sealed housing or vessel contains an electric motor drivingly connected by said shaft assembly with a hydraulic pump in said first sealed housing or vessel, said first sealed housing or vessel forming a hydraulic reservoir for said pump which is operable to actuate a servo motor, said connector including a flameproof path for the passage of air therethrough.
 10. An arrangement as claimed in claim 9, wherein said servo motor operates an output member. 